The present invention involves a novel design for a printed circuit board (PCB) substrate drilling apparatus that greatly increases the speed and accuracy in repetitive commercial drilling as well as minimizing the wander of the drill bits, the breakage of the drill bits and extending the life of the drill bits. This is accomplished by improving the machine dynamics.
There is a huge industry developed around the demand to drill multiple, spaced holes (through or non-through) in substrates such as electronic wafers, thin film electronics, organic packaging substrates or the like. Large, commercial PCB drilling systems quickly position and operate these drilling apparatuses. These holes or patterned drillings may be used for electrical connections, filtration, cytology, bioassays, chemotoxis, or particle monitoring and have diameters that commonly lie in the micron range. Not only must the holes be identical to each other in diameter but also must be placed at precise locations and with the right geometry with respect to the substrate or adjacent holes.
Generally, such drilling systems see movement in all three axes. There is simultaneous movement in the x and y axes (horizontal plane) by a linear beam style, y-axis wing and x-axis carriage that places a drilling apparatus precisely over a substrate to be drilled. A z-axis (vertical axis) drilling apparatus mounted on the x-axis carriage then momentarily plunges a high speed revolving drill bit into the substrate to drill a hole, once the y-axis wing and x-axis carriage reaches the specified position window (the precise location within set dimensional tolerances), and then the cycle repeats itself. There are usually multiple carriages on the wing, each with their own drilling apparatus to enable simultaneous drilling of a plethora of substrates. The proper positioning of the drilling apparatus is accomplished using a set of linear scales (optical or magnetic positioning sensors.) This positioning prior to drilling occurs extremely rapidly by computer control, cycling up to thousands of times per minute.
Pursuant to Newton's third law of motion, each of these three positioning or drilling movements creates reactionary forces in the structure of the PCB substrate drilling system. The size of these reactionary forces is directly related to the magnitude of the moving mass of the wing, carriage and the drilling apparatus. Generally commercial machines try to make the stationary mass to moving mass ratio of their systems greater than 10:1. In the system that incorporates this present invention, this ratio exceeds 22:1.
The settling or lag time for the linear scales to report that the drilling apparatus is positioned within the acceptable tolerance ranges (positioning window) to initiate the plunge drilling, is slowed by the reactionary forces. Thus, the magnitude of the moving mass, slows the positioning process and adds slight inaccuracies in the z-axis drilling apparatus's positioning. This limits the productivity of the PCB drilling system.
All the prior art PCB substrate drilling systems incorporate specialized designs to minimize these reactionary forces. The state of this art is highly developed and further advances in this area are slow. The secret to higher output lies in reducing the mass of the moving components, and eliminating any unbalanced forces.
Henceforth, a PCB substrate drilling system with improved accuracy and speed, faster and deeper drilling depth (increased PCB substrate stack heights), longer drill bit life, less drill bit breakage and a higher machine throughput would fulfill a long felt need in the substrate drilling and surface patterning industry. This new invention utilizes a low mass, low profile, dynamic force balanced z-axis drilling apparatus to reduce reactionary forces and combines known and new technologies in a unique and novel configuration to overcome the aforementioned problems of the prior art PCB drilling systems.